Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J29/00—Catalysts comprising molecular sieves
  • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
  • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
  • B01J29/65—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the ferrierite type, e.g. types ZSM-21, ZSM-35 or ZSM-38, as exemplified by patent documents US4046859, US4016245 and US4046859, respectively
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C5/00—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms
  • C07C5/22—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms by isomerisation
  • C07C5/27—Rearrangement of carbon atoms in the hydrocarbon skeleton
  • C07C5/2767—Changing the number of side-chains
  • C07C5/277—Catalytic processes
  • C07C5/2775—Catalytic processes with crystalline alumino-silicates, e.g. molecular sieves
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2229/00—Aspects of molecular sieve catalysts not covered by B01J29/00
  • B01J2229/10—After treatment, characterised by the effect to be obtained
  • B01J2229/26—After treatment, characterised by the effect to be obtained to stabilize the total catalyst structure
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2229/00—Aspects of molecular sieve catalysts not covered by B01J29/00
  • B01J2229/30—After treatment, characterised by the means used
  • B01J2229/42—Addition of matrix or binder particles

Definitions

• This invention relates to a method for the selective conversion of linear olefins to corresponding iso-olefins of the same carbon number.
• the demand for iso-alkenes has recently increased.
• MTBE methyl tert-butyl ether
• ETBE ethyl tert-butyl ether
• Isoamylenes are required for reaction with methanol over an acidic catalyst to produce tert-amyl methyl ether (TAME) .
• TAME tert-amyl methyl ether
• Isobutene (or isobutylene) is in particularly high demand as it is reacted with methanol to produce MTBE.
• shape-selective zeolite additives such as ZSM-5 to cracking catalysts, e.g.
• the reaction of tertiary olefins with alkanol to produce alkyl tertiary alkyl ether is selective with respect to iso-olefins.
• Linear olefins are unreactive in the acid catalyzed reaction, even to the extent that it is known that the process can be utilized as a method to separate linear and iso-olefins.
• the typical feedstream of FCC C4 or C4+ crackate used to produce tertiary alkyl ethers in the prior art which contains normal butene and isobutene utilizes only the branched olefin in etherification. This situation presents an exigent challenge to workers in the field to discover a technically and economically practical means to utilize linear olefins, particularly normal butene, in the manufacture of tertiary alkyl ethers.
• linear olefins can be restructured in contact with zeolite catalyst, including Theta-1 (ZSM-22) and ZSM- 23, to produce branched olefins.
• the restructuring conditions comprise temperature between 200-550oC, pressure between 100 and 5000 kPa and WHSV between 1 and 100.
• Selectivities to isobutene up to 91.2% are reported using a calcined Theta-1 tectometallosilicate at 400°C and 30.6% 1-butene conversion.
• U.S. Patent No. 4,922,048 discloses the use of a wide variety of medium pore size zeolites, e.g. ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35 and ZSM-48, in low temperature (232-385°C) olefin interconversion of C2-C6 olefins to products including tertiary C4-C5 olefins and olefinic gasoline.
• medium pore size zeolites e.g. ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35 and ZSM-48.
• U.S. Patent No. 4,886,925 discloses low pressure high temperature conversion of light olefins to produce higher olefins rich in isoalkenes.
• the process converts C2+ n-alkenes to a product comprising C4-C6 alkenes rich in iso-alkenes, C7+ olefinic gasoline boiling range hydrocarbons, and unconverted hydrocarbons over ZSM-5.
• the reference teaches further treatment of the alkene effluent with methanol in the presence of medium pore size zeolites such as ZSM-5, ZSM-11, ZSM-12, ZSM-35, and ZSM-48.
• U.S. Patent No. 4,996,386 discloses concurrent isomerization and disproportionation of olefins using a ferrierite/Mo/W/Al203 catalyst.
• the catalyst exemplified produces fewer branched olefins than a comparable material free of ferrierite and the reference teaches that ferrierite-containing catalysts exhibit improved selectivity to linear olefins than conventionally prepared disproportionation catalysts.
• the skeletal isomerization of olefins e.g., to produce isobutene, has been hampered by relatively low selectivity to isobutene perhaps owing to the lability of these olefins.
• Selectivities of greater than 90%, 95% or even 99% are highly advantageous in commercial conversion of n-butenes to isobutene in order to avoid the need to separate out materials other than n-butene from the product stream.
• Such high selectivities will permit direct introduction (cascading) or indirect introduction of the isomerizer effluent to an etherification zone where isobutene is reacted with alkanol to produce alkyl tert-butyl ether, e.g. MTBE.
• Unconverted n-butenes in the isomerizer effluent can be withdrawn either before the etherifica- tion zone or preferably, from the etherification zone effluent insofar as the etherification reaction utilizes only the isobutene component of the isomerizer stream. Unreacted n-butenes from the etherification zone effluent can be recycled to the isomerizer where they are converted to isobutene at high selectivity. If the recycle stream contains not only unconverted linear olefins, e.g. n-butenes, but also by-product such as other olefins (e.g.
• propylene or paraffins
• they have to be removed from the recycle stream, such as by distillation or by taking a slip stream.
• These removal steps are expensive and can lead to considerable loss of not only the by-products but butenes as well. These losses are larger when the by-products formed are present in higher concentration.
• high selectivities in skeletal isomerization processes have generally required low linear olefin partial pressures and high temperatures which place substantial limitations on such processes. It would, therefore, be advantageous to provide a skeletal isomerization catalyst capable of maintaining relatively high selectivity at low temperatures and high linear olefin partial pressures.
• the present invention provides a method for highly selective conversion of linear olefins to corresponding iso-olefins of the same carbon number, e.g. n-butenes to isobutene, which comprises contacting a linear olefin-containing organic feedstock with a catalyst comprising ZSM-35 .
• the catalyst comprises microcrystal- line ZSM-35, by which is meant that the zeolite has a crystal morphology whose largest dimension is no greater than 0.5 micron, and whose ratio of its second largest dimension to said largest dimension ranges from about 0.5 to 1.
• the ZSM-35 is composited with a silica-containing matrix so that the catalyst composite has a total pore volume of at least 0.6 cc/g or 300+ angstroms pore volume of at least 0.1 cc/g.
• the high selectivity of ZSM-35 in the present invention results in large part from isomerization occurring without significant conversion to lighter and heavier molecules. This phenomenon, it is believed, is a consequence of the pore structure of ZSM-35 which promotes isomerization at a much faster rate than the reaction by which, e.g. butene, is converted to lighter (mostly propylene) and heavier olefins (olefin interconversion reaction) . Moreover, such isomeriza ⁇ tion takes place without significant cracking of the feed or hydrogenation or dehydrogenation effects resulting in the formation of, say, n-butane or butadiene.
• the present invention can be used to effect conversion of linear olefins to iso-olefins while resulting in less than 30%, 10%, 5% or even less than 1% by weight of converted product having lower or higher average carbon number.
• microcrystalline ZSM-35 allows the highly selective olefin isomerization of the present invention to be conducted at higher conversion levels.
• a highly porous, silica-bound catalyst composite reduces catalyst aging.
• the skeletal isomerization reaction of the present invention is carried out at temperatures of from 100 to 750°C, weight hourly space velocity based on linear olefin in the feed of from 0.1 to 500 and linear olefin partial pressures of from 2 to 2000 kPa.
• the preferred conditions are a temperature of 150 to 600°C, most preferably 200 to 550°C; weight hourly space velocity based on linear olefin in the feed of 0.5 to 400, most preferably 1 to 100; and a linear olefin partial pressure of 10 to 500 kPa, most preferably 20 to 200 kPa.
• linear olefin e.g., n-butene
• conversion of linear olefin can be at least 10%, preferably at least 35% and more preferably at least 45%.
• the selectivity to iso-olefin, e.g., isobutene is at least 75%, preferably at least 85%, 90%, or even 95%.
• Preferred feedstreams include C4 or C4+ hydrocarbon feedstreams.
• Linear olefins suited for use in the present invention may be derived from a fresh feedstream, preferably comprising n-butenes and/or n- pentenes, or from the effluent of an iso-olefin etherification reactor which employs alkanol and C4 or C4+ hydrocarbon feedstock.
• Typical hydrocarbon feedstock materials for isomerization reactions according to the present invention include olefinic streams, such as cracking process light gas containing butene isomers in mixture with substantial amounts of paraffins including n-butane and isobutane.
• the C4 components usually contain a major amount of un- saturated compounds, such as 10-40% isobutene, 20-55% linear butenes, and small amounts of butadiene.
• C4+ heavier olefinic hydrocarbon streams may be used, e.g C4 to CIO, preferably C4 to C6 olefinic hydrocarbon streams.
• the process of the invention employs a catalyst comprising the zeolite ZSM-35.
• ZSM-35 is more particularly described in U.S. Patent No. 4,016,245.
• "ZSM-35" is considered equivalent to its isotypes, which include ferrierite (P.A. Vaughan, Acta Cryst. 21, 983 (1966)); FU-9 (D.
• the ZSM-35 used in the process of the invention is in a microcrystalline form in that it has a morphology whose largest dimension is no greater than 0.5 micron, preferably no greater than 0.25 micron and more preferably no greater than 0.15 micron, and whose ratio of its second largest dimension to its largest dimension is 0.5 to 1.0.
• the ZSM-35 crystals can be described as falling within the range of 0.03 to 0.08 micron by 0.03 to 0.08 micron by ⁇ 0.05 micron.
• Microcrystalline ZSM-35 is made by control of the synthesis formulation and synthesis temperature, with lower temperature favoring smaller crystals.
• the zeolite catalyst used is preferably at least partly in the hydrogen form, e.g., HZSM-35, but other cations, e.g., rare earth cations, may also be present.
• the zeolites When the zeolites are prepared in the presence of organic cations, they may be quite inactive possibly because the intracrystalline free space is occupied by the organic cations from the forming solution.
• the zeolite may be activated by heating in an inert atmosphere to remove the organic cations e.g., by heating at over 500°C for 1 hour or more.
• the hydrogen form can then be obtained by base exchange with ammonium salts followed by calcination e.g., at 500°C in air.
• Other cations, e.g., metal cations can be introduced by conventional base exchange or impregnation techniques.
• the ZSM-35 should have an alpha value of at least 5, preferably at least 50 when used in the catalyst of the present invention.
• Alpha value, or alpha number, of a zeolite is a measure of zeolite acidic functionality and is more fully described together with details of its measurement in U.S. Patent No. 4,016,218, J. Catalysis. 6_, pp. 278-287 (1966) and J. Catalysis. 61. pp. 390-396 (1980) .
• the ZSM-35 may be incorporated in another material usually referred to as a matrix or binder.
• matrix materials include synthetic or naturally occurring substances as well as inorganic materials such as clay, silica and/or metal oxides. The latter may be either naturally occurring or in the form of gelatinous precipitates or " gels including mixtures of silica and metal oxides.
• Naturally occurring clays which can be composited with the zeolite include those of the montmorillonite and kaolin families, which families include the subbentonites and the kaolins commonly known as Dixie, McNamee, Georgia and Florida clays or others in which the main mineral constituent is halloysite, kaolinite, dickite, nacrite or anauxite. Such clays can be used in the raw state as originally mined or initially subjected to calcination, acid treatment or chemical modification.
• the zeolites employed herein may be composited with a porous matrix material, such as silica, alumina, zirconia, titania, silica-alumina, silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia, silica-titania as well as ternary compositions such as silica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesia and silica-magnesia-zirconia.
• the matrix can be in the form of a cogel. A mixture of these components could also be used.
• the relative proportions of finely divided ZSM-35 and inorganic oxide gel matrix may vary widely with the zeolite content ranging from 1 to 90 percent by weight and more usually in the range of 30 to 80 percent by weight of the composite.
• silica is preferred as the matrix material owing to its relative inertness for catalytic cracking reactions which are preferably minimized in the instant isomerization processes.
• silica-containing matrix containing a minor amount of aluminum may be employed.
• a silica binder and controlling extrusion conditions by means such as moisture control to ensure increased pore volume results in a catalyst which ages more slowly under skeletal isomerization conditions, resulting in increased cycle length.
• Such conditions increase total pore volume to greater than 0.6 g/cc, or 300 angstroms pore volume to greater than 0.1 cc/g.
• These increased pore volumes can be obtained by increasing moisture content of the extrudate.
• the resulting catalyst composite is of particular utility insofar as its use can result in increased cycle length without any significant loss of iso-olefin selectivity.
• the regeneration of spent zeolite catalyst used in the isomerization reaction is carried out oxidatively or hydrogenatively employing procedures known in the art.
• the catalyst of the present invention can be readily reactivated without significantly reducing selectivity for isobutene by exposing it to hydrogen for a suitable period, e.g. overnight.
• Figure 1 depicts the respective conversions and products obtained for ZSM-22, ZSM-23 and ZSM-35 in skeletal isomerization of 1-butene at 550°C.
• Figure 2 depicts the respective conversions and products obtained for ZSM-22, ZSM-23 and ZSM-35 in skeletal isomerization of 1-butene at 400 ⁇ C.
• Figure 3 is a selectivity/conversion plot comparing the performance of ZSM-23 and ZSM-35.
• Figure 4 depicts the conversions and products obtained for ZSM-35 in skeletal isomerization of 1- butene at high WHSV, low temperatures and high butene partial pressures.
• Figure 5 is a transmission electron microscopy (TEM) micrograph of a microcrystalline ZSM-35 sample prepared in accordance with the procedure set out in Example 1.
• Figure 6 is a transmission electron microscopy (TEM) micrograph of large crystal ZSM-35 of Example 12.
• Figure 7 is a transmission electron microscopy (TEM) micrograph of large crystal synthetic ferrierite of Example 13.
• Figure 8 depicts 1-butene conversion and iso-butene selectivity over temperature at 165 WHSV from Example 14.
• Figure 9 depicts 1-butene conversion and iso-butene selectivity over temperature at 2 WHSV from Example 15.
• Figure 10 depicts the low aging rate of microcrystalline ZSM-35 compared to large crystal synthetic ferrierite where n-butene conversion is plotted as a function of cumulative 1-butene throughput.
• Figure 11 compares the aging rates of alumina-bound ZSM-35 catalyst from Example 16 and silica-bound ZSM-35 catalyst of enhanced pore volume from Example 17.
• Figure 12 compares selectivity versus conversion in n-butene conversion for the alumina-bound catalyst of Example 16 and the silica-bound catalyst of enhanced pore volume from Example 17.
• Figure 13 compares the effects of binder pore size on ZSM-35 aging in butene skeletal isomerization for the small pore silica-bound catalyst of Example 4, versus the large-pore silica-bound catalyst of Example 17.
• Figure 14 compares selectivity versus conversion for the small pore silica-bound catalyst of Example 4, compared with the large-pore silica-bound catalyst of Example 17.
• EXAMPLE 1 Preparation of Microcrystalline ZSM-35
• the reaction mixture had the following composition, in mole ratios:
• the chemical composition of the product was, in weight percent:
• the as-synthesized ZSM-35 of Example 1 was calcined in nitrogen for 3 hours at 538°C, then exchanged two times at room temperature with 1 N NH4N03 solution to convert it to the ammonium form, dried at 120°C, and calcined in air for 6 hours at 538°C to convert it to the hydrogen form.
• the zeolite was dry mixed with a precipitated silica, in proportion to give 65% ZSM-35 / 35% silica after calcination, formed into pellets, and calcined in air for 3 hours at 538°C.
• EXAMPLE 4 Preparation of Silica-Bound HZSM-35 A catalyst was prepared by dry mixing the as- synthesized ZSM-35 of Example 1 with precipitated silica. Colloidal silica, in proportion to give 65% ZSM-35 / 35% silica after calcination, and water were added to the dry mix to obtain an extrudable mull. The mull was extruded to 1/16 inch (1.6 mm) diameter, dried at 120 ⁇ C, calcined in nitrogen for three hours at 538°C, and then in air for 6 hours at 538°C. The extrudate was exchanged two times with IN NH4N03 solution at room temperature, dried at 120"C and calcined in nitrogen for 3 hours at 538°C. The total pore volume of this catalyst was 0.55 cc/g and 300 angstrom pore volume was 0.04 cc/g.
• ZSM-35 at 550°C ZSM-22 was prepared by charging 48.2 parts water to an autoclave followed by 5.0 parts KOH solution (45% by weight), 1.0 part aluminum sulfate (17.2% A1203) and 0.45 parts seeds. After mixing thoroughly, 8.2 parts of Ultrasil VN3 precipitated silica (Nasilco), then 3.6 parts of ethylpyridinium bromide (50% by weight) were added and mixed thoroughly. After aging the reaction mixture for 16 hours at 93°C while stirring, the temperature was increased to 160"C and maintained until crystallization was complete. The product was identified as ZSM-22 by X-ray diffraction. The slurry was filtered, washed and dried.
• a portion of the zeolite was calcined in flowing nitrogen for 3 hours at 538°C and 3 hours in air at the same temperature.
• the cooled zeolite was exchanged with 1 N NH4N03 (5 cc/g zeolite) at room temperature for one hour then washed with water. The exchange procedure was repeated and the catalyst dried at 120°C.
• the zeolite was then calcined in flowing air for 3 hours at 538 ⁇ C, then blended 65 parts zeolite and 35 parts Ultrasil VN3 and pelleted. The pellets were sized 14/24 mesh and recalcined at 538°C in flowing air for 3 hours.
• ZSM-23 was prepared by charging 85.5 parts water to an autoclave followed by 2.64 parts KOH solution (45% by weight), 1.0 part aluminum sulfate (17.2% A1203) and 0.5 parts ZSM-23 seeds (100% basis). After mixing thoroughly, 14.5 parts of Ultrasil VN3 precipitated silica (Nasilco), then 5.1 parts of pyrrolidine were added and mixed thoroughly. The autoclave was heated to 160"C with stirring and maintained at these conditions until crystallization was complete. The product was identified as ZSM-23 by X-ray diffraction. After flashing the pyrrolidine, the slurry was cooled, washed, filtered and dried. Eight parts of the dried ZSM-23 were combined with 1 part Ultrasil VN3 and 1 part Ludox colloidal silica
• N2/Butene in feed 3 vol/vol Figure 1 graphically depicts the respective conversions and products obtained for ZSM-22, ZSM-23 and ZSM-35. Under these conditions selectivities of 83.5%, 88.2% and 95%, respectively, were obtained.
• EXAMPLE 6 Isomerization of 1-Butene with ZSM-22, ZSM-23 and
• N2/Butene in feed 3 vol/vol Figure 2 graphically depicts the respective conversions and products obtained for ZSM-22, ZSM-23 and ZSM-35. Under these conditions selectivities of 54.3%, 51.1% and 93.2%, respectively, were obtained. ZSM-35 maintains selectivity above 90% even at temperatures which significantly reduce selectivities for ZSM-22 and ZSM-23.
• FIG. 3 is a selectivity/conversion plot comparing the performance of the two catalysts. At 30 to 40% conver ⁇ sion, selectivity of ZSM-23 ranges of from 30 and 80%. In contrast, selectivity of ZSM-35 ranges from 90 to
• the ZSM-35-containing catalyst of Example 2 was used to process a 1-butene feed under four sets of skeletal isomerization conditions comprising two temperatures and two relatively low 1-butene partial pressures.
• the conditions and compositions of the product streams from Runs 1 to 4 are set out in Table 1 below. Selectivity for isobutene ranged from 93.2 to 99%.
• the ZSM-35-containing catalyst of Example 3 was used to process a 1-butene feed under four sets of skeletal isomerization conditions comprising two temperatures and two relatively low 1-butene partial pressures.
• the conditions and compositions of the product streams from Runs 1 to 4 are set out in Table 2 below.
• a comparison of Tables 1 and 2 shows that silica binding has no significant deleterious effect on performance between silica-bound ZSM-35 and ZSM-35/Si02 mix catalysts.
• EXAMPLE 13 Large Crystal Synthetic Ferrierite
• a synthetic ferrierite obtained from Tosoh had a silica to alumina molar ratio of 16.8/1, an alpha value of 81, and a surface area of 219 m 2/g. Scanning electron microscopy and transmission electron microscopy indicate the synthetic ferrierite crystals have platelet morphology with a broad distribution of crystal sizes having the largest dimension of up to 1 to 2 microns.
• Figure 7 is a TEM micrograph of the large crystal synthetic ferrierite thus prepared. The synthetic ferrierite was dry mixed with precipitated silica in a ratio to achieve 65% ferrierite/35% silica after processing.
• microcrystalline ZSM-35 of Example 4 and the large crystal ZSM-35 of Example 12 were used in 1-butene skeletal isomerization reactions carried out at 300, 400, 500 and 550"C, and at 165 WHSV, 30 psia.
• 1-Butene conversion and iso-butene selectivity over temperature are depicted in Figure 8. Significantly higher n-butene conversions occur with microcrystalline ZSM-35 with no loss of isobutene selectivity.
• Synthetic Ferrierite The synthetic ferrierite of Example 13 was used in 1-butene skeletal isomerization reactions carried out at 400 to 500°C, 66 WHSV, 24 psia, using a nitrogen/1-butene feed. The conditions of each run and the product composition is set out below in Table 3. At 400°C, conversion was near zero (0.34%). Conversion did not increase even when temperature was raised to 550"C and WHSV reduced to 33. Conversion did increase to 50-60% when WHSV was cut to 2 as depicted in Figure 9. However, selectivity was low (60-70%) and the cata ⁇ lyst aged rapidly.
• a catalyst was prepared by dry mixing the as-synthesized ZSM-35 of Example 1 with alumina (LaRoche Versal 250) such that the final product contained 65 parts ZSM-35 and 35 parts alumina. Sufficient water was added to obtain a mixture which was extruded to 1/16 inch (1.6 mm) diameter pellets then dried at 100°C. The extrudate was calcined in nitrogen at 538°C for three hours, then exchanged twice with a 1 N NH.N0_ solution at room temperature, dried at 100°C and calcined in air for 6 hours. The product had a pore volume of 0.86 cc/g and a 300 angstrom pore volume of 0.46 cc/g. EXAMPLE 17
• a catalyst was prepared by dry mixing the as-synthesized ZSM-35 of Example 1 with precipitated silica (Ultrasi .lTM VNSP3 from Degussa) . Colloidal silica, in proportion to give 65% ZSM-35 / 35% silica after calcination, and water were added to the dry mix to obtain an extrudable mixture. The mix was extruded to 1/16 inch (1.6 mm) diameter pellets, and dried at 100"C.
• precipitated silica Ultrasi .lTM VNSP3 from Degussa
• the extrudate was calcined in nitrogen at 538°C for three hours, then exchanged twice with a 1 N NH.NO solution at room temperature, dried at 100°C and calcined in air for 7 hours.
• the product had a pore volume of 0.86 cc/g and a 300 angstrom pore volume of 0.37 cc/g.
• Figure 11 compares the effects of aging on n-butene conversion for the alumina-bound catalyst of Example 16, versus the silica-bound catalyst of Example 17, showing a reduction in activity from 46% to 23% n-butene conversion over about 7 days compared with a reduction in activity from 47% to 30% n-butene conversion over about 18 days, respectively.
• Figure 12 compares the effects of n-butene conversion on isobutene selectivity for n-butene conversion for the alumina-bound catalyst of Example 16, versus the silica-bound catalyst of Example 17. The results show little variation in isobutene selectivity over a range of about 23 to 50% n-butene conversion between the two catalyst types.
• Figure 13 compares the effects of aging for the silica-bound catalyst of Example 4, versus the silica-bound catalyst of Example 17, showing a reduction in activity from 48% to 28% n-butene conversion over about 12 days compared with a reduction in activity from 47% to 30% n-butene conversion over about 18 days, respectively.
• Figure 14 compares the effects of reduced n-butene conversion (aging) on isobutene selectivity on n-butene conversion for the silica-bound catalyst of Example 4, versus the silica-bound catalyst of Example 17. The results show little variation in isobutene selectivity over a range of about 28 to 50% n-butene conversion between the two catalyst types.

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